98 sierra with no brake or flashing lights but has reverse lights

98 sierra truck has no brake lights or turn signals in back but reverse lights work need help on what is wrong. I checked fuses and relay under hood. lights are plugged in at back, and has bulbs in that are not blown. Anybody?

check ground wire near rear bumper had same problem on my 1990 gmc 1/2 ton truck. i cleaned up frame and hooked wire back on and everything worked